Structural and magnetotransport properties of ultrathin Co/ZnO and Co/ZnAlO films

We report the structural and magnetotransport properties of ultrathin superparamagnetic Co/ZnO and Co/ZnAlO films deposited by sequentially sputtering Co layers and semiconductor layers. The films consisting of Co nanodots embedded in an amorphous semiconductor matrix exhibit large room temperature tunneling magnetoresistance with a maximum value of over 7%. The single-layer-nanodot structures gradually develop in the films with thicknesses below 8 nm, where tunneling processes existing only between nanodots that lie in a plane are realized. The tunneling magnetoresistance ratio at room temperature is as high as 5% although the thickness of the Co/ZnAlO film is as thin as 3.2 nm. These single-layer-nanodot films having high tunneling magnetoresistance ratios and superparamagnetic behavior can be used in transparent nano-granular in gap sensors.